1991–92 South-West Indian Ocean cyclone season
The 1991–92 South-West Indian Ocean cyclone season was an average cyclone season in which most storms remained over open waters. At the time, the season's official bounds lasted from November 15, 1991, to April 30, 1992, although this season began early when three tropical depressions formed before the official start. The second, designated Tropical Depression A2 by the Météo-France office on Réunion, passed north of Madagascar on October 16 before weakening.
The first named storm was Severe Tropical Storm Alexandra, which developed on December 18 from the monsoon trough; many other storms during the year originated in this manner. Tropical Storm Bryna was the only tropical storm of the season to make landfall, having struck northeastern Madagascar on January 2. The basin was most active in February, when five named storms developed, including Tropical Depression Elizabetha which struck western Madagascar. In early March, Cyclone Harriet entered the basin from the Australian region and was renamed Heather. It intensified to peak winds of, making Heather the strongest storm of the season. In April, another cyclone - Jane - crossed from the Australian region and was renamed Irna, which reentered the Australian region on April 19 to end tropical activity within the basin.
Season summary
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In general, sea surface temperatures were warmest near the equator in the northeast portion of the basin, and in the Mozambique Channel between Mozambique and Madagascar. During the season, the Météo-France office on Réunion island issued warnings in tropical cyclones within the basin. The agency estimated intensity through the Dvorak technique, and warned on tropical cyclones in the region from the coast of Africa to 80° E, south of the equator. The Joint Typhoon Warning Center, which is a joint United States Navy – United States Air Force task force, also issued tropical cyclone warnings for the southwestern Indian Ocean.
During the season, there was an El Niño event that caused tropical cyclogenesis in the southern hemisphere to shift more to the east. In addition, the monsoon trough, which helped spawn most of the storms in the season, was weaker than normal in the Indian Ocean. The number of tropical depressions forming was above average, although there were fewer days than normal with tropical cyclone activity.
Systems
Tropical Storm 01S
On September 10, 1991, the JTWC began monitoring a tropical depression in the northeastern portion of the basin. The system moved southeastward, and according to the agency intensified into an 85 km/h tropical storm on September 12. By the next day, the storm dissipated after turning back to the north.Tropical Depression A2
About a month after the previous storm dissipated, the JTWC classified another tropical depression on October 11 about 960 km east-southeast of Seychelles. The system tracked west-southwestward, and the MFR also began issuing warnings on it as Tropical Depression A2 on October 14. Two days later, the JTWC briefly upgraded the depression to a tropical storm, although MFR only estimated peak 10‑minute winds of. By that time, the storm had turned to the west, passing north of the northern tip of Madagascar. After turning to the west-northwest, the depression dissipated on October 22.Moderate Tropical Storm A4
On November 20, the JTWC began tracking Tropical Cyclone 04S a short distance southeast of Diego Garcia. The next day, MFR also initiated advisories on it, classifying the system as Tropical Depression A4. After moving southwestward initially, the storm curved south-southeastward and intensified. The JTWC estimated peak 1‑minute winds of 85 mph, and the MFR estimated 10‑minute winds of, indicating that it could have been named. While near peak intensity, the storm was affected by wind shear that displaced the circulation center along the north edge of the convection. The storm turned to the west, passing just south of St. Brandon before dissipating on November 29.Severe Tropical Storm Alexandra
On December 17, the JTWC began monitoring a tropical depression about 700 km west of Diego Garcia in association with the Intertropical Convergence Zone, designating it as Tropical Cyclone 09S. The next day, the MFR also began classifying the system. The nascent depression moved generally to the southeast, and later more to the south-southeast, ahead of an approaching upper-level trough. On December 20, the depression intensified into Tropical Storm Alexandra, and that day developed an ill-defined eye, as well as good inflow. The JTWC upgraded Alexandra to the equivalent of a minimal hurricane - with 1-minute sustained winds of at least on December 21, but MFR only estimated peak 10‑minute winds of. Although the MFR estimated the storm subsequently weakened, the JTWC assessed that Alexandra continued to intensity to a peak 1‑minute intensity of on December 22. Around that time, the cyclone had slowed and turned to the east. Increased shear caused gradual weakening, and the strengthening of the subtropical ridge turned Alexandra to the southwest. The JTWC discontinued advisories on December 26, and Alexandra dissipated three days later well to the east-northeast of Mauritius, or about 1,600 km south of where it first formed.Moderate Tropical Storm Bryna
The MFR began monitoring a tropical depression on December 25 about 900 km east-northeast of the northern tip of Madagascar. Initially moving eastward without any strengthening, the depression turned back to the west toward Madagascar on December 28 due to a ridge. Two days later, the JTWC also began tracking the system, designating it as Tropical Cyclone 10S. With warmer water temperatures but persistent wind shear, the system strengthened into Tropical Storm Bryna on December 31. At 1800 UTC that day, the MFR estimated peak 10‑minute winds of. On January 1, the JTWC estimated peak 1‑minute winds of, before assessing that Bryna began weakening. The storm made landfall in the Sava Region of eastern Madagascar early on January 2 and subsequently crossed the northern portion of the country. Although the JTWC discontinued advisories while Bryna was inland, the MFR continued tracking it, and the circulation emerged into the Mozambique Channel on January 3, moving around a ridge. Bryna curved to the south, brushing Melaky before moving farther offshore. The MFR estimated a secondary peak intensity of on January 7, based on ship reports, although the structure was more subtropical in nature. Around that time, Bryna was turning to the southeast, and the next day made a final landfall in southwestern Madagascar. After crossing the southern portion of the country, Bryna moved over open waters, eventually turning back to the southwest before dissipating on January 10.While moving over Madagascar, Bryna dropped heavy rainfall, causing some damage and two deaths in Mahajanga.